Are you still able to boot the phone into the TWRP recovery of Fairphone Open OS (Volume Up when starting or rebooting)?
If so, you might try installing Fairphone OS via TWRP using these files …
(Be aware that as I read it, you need to install two files in succession this way to get to the current OS version … the “FP2 - Update file of Fairphone OS 1.13.0” file and then the “FP2 - Update file of Fairphone OS 18.01.1 from 1.13.0” file, as the 1.13.0 file is the last complete OTA file given there, even it is called an update, everything else are really just updates from another version. Don’t boot in between, just queue the two files in TWRP for installing and then flash them in one go.)
By the way … do you have a backup of your important data 
?